/* 
 * tsh - A tiny shell program with job control
 * 
 * <Put your name and login ID here>
 * 戴茗静 3023244157
 */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <errno.h>

/* Misc manifest constants */
#define MAXLINE    1024   /* max line size */
#define MAXARGS     128   /* max args on a command line */
#define MAXJOBS      16   /* max jobs at any point in time */
#define MAXJID    1<<16   /* max job ID */

/* Job states */
#define UNDEF 0 /* undefined */
#define FG 1    /* running in foreground */
#define BG 2    /* running in background */
#define ST 3    /* stopped */

/* 
 * Jobs states: FG (foreground), BG (background), ST (stopped)
 * Job state transitions and enabling actions:
 *     FG -> ST  : ctrl-z
 *     ST -> FG  : fg command
 *     ST -> BG  : bg command
 *     BG -> FG  : fg command
 * At most 1 job can be in the FG state.
 */

/* Global variables */
extern char **environ;      /* defined in libc */
char prompt[] = "tsh> ";    /* command line prompt (DO NOT CHANGE) */
int verbose = 0;            /* if true, print additional output */
int nextjid = 1;            /* next job ID to allocate */
char sbuf[MAXLINE];         /* for composing sprintf messages */

struct job_t 
{              /* The job struct */
    pid_t pid;              /* job PID */
    int jid;                /* job ID [1, 2, ...] */
    int state;              /* UNDEF, BG, FG, or ST */
    char cmdline[MAXLINE];  /* command line */
};
struct job_t jobs[MAXJOBS]; /* The job list */
/* End global variables */


/* Function prototypes */

/* Here are the functions that you will implement */
void eval(char *cmdline);
int builtin_cmd(char **argv);
void do_bgfg(char **argv);
void waitfg(pid_t pid);

void sigchld_handler(int sig);
void sigtstp_handler(int sig);
void sigint_handler(int sig);

/* Here are helper routines that we've provided for you */
int parseline(const char *cmdline, char **argv); 
void sigquit_handler(int sig);

void clearjob(struct job_t *job);
void initjobs(struct job_t *jobs);
int maxjid(struct job_t *jobs); 
int addjob(struct job_t *jobs, pid_t pid, int state, char *cmdline);
int deletejob(struct job_t *jobs, pid_t pid); 
pid_t fgpid(struct job_t *jobs);
struct job_t *getjobpid(struct job_t *jobs, pid_t pid);
struct job_t *getjobjid(struct job_t *jobs, int jid); 
int pid2jid(pid_t pid); 
void listjobs(struct job_t *jobs);

void usage(void);
void unix_error(char *msg);
void app_error(char *msg);
typedef void handler_t(int);
handler_t *Signal(int signum, handler_t *handler);

/*
 * main - The shell's main routine 
 */
int main(int argc, char **argv) 
{
    char c;
    char cmdline[MAXLINE];
    int emit_prompt = 1; /* emit prompt (default) */

    /* Redirect stderr to stdout (so that driver will get all output
     * on the pipe connected to stdout) */
    dup2(1, 2);

    /* Parse the command line */
    while ((c = getopt(argc, argv, "hvp")) != EOF)
    {
        switch (c) 
        {
            case 'h':             /* print help message */
                usage();
	            break;
            case 'v':             /* emit additional diagnostic info */
                verbose = 1;
	            break;
            case 'p':             /* don't print a prompt */
                emit_prompt = 0;  /* handy for automatic testing */
	            break;
	        default:
                usage();
	    }
    }

    /* Install the signal handlers */

    /* These are the ones you will need to implement */
    Signal(SIGINT,  sigint_handler);   /* ctrl-c */
    Signal(SIGTSTP, sigtstp_handler);  /* ctrl-z */
    Signal(SIGCHLD, sigchld_handler);  /* Terminated or stopped child */

    /* This one provides a clean way to kill the shell */
    Signal(SIGQUIT, sigquit_handler); 

    /* Initialize the job list */
    initjobs(jobs);

    /* Execute the shell's read/eval loop */
    while (1) 
    {

	    /* Read command line */
	    if (emit_prompt) 
        {
	        printf("%s", prompt);
	        fflush(stdout);
	    }
	    if ((fgets(cmdline, MAXLINE, stdin) == NULL) && ferror(stdin))
	        app_error("fgets error");
	    if (feof(stdin)) 
        { /* End of file (ctrl-d) */
	        fflush(stdout);
	        exit(0);
	    }

	    /* Evaluate the command line */
	    eval(cmdline);
	    fflush(stdout);
	    fflush(stdout);
    } 

    exit(0); /* control never reaches here */
}
  
/* 
 * eval - Evaluate the command line that the user has just typed in
 * 
 * If the user has requested a built-in command (quit, jobs, bg or fg)
 * then execute it immediately. Otherwise, fork a child process and
 * run the job in the context of the child. If the job is running in
 * the foreground, wait for it to terminate and then return.  Note:
 * each child process must have a unique process group ID so that our
 * background children don't receive SIGINT (SIGTSTP) from the kernel
 * when we type ctrl-c (ctrl-z) at the keyboard.  
*/
void eval(char *cmdline) 
{ 
    //相关定义和初始化
    int state=UNDEF;
    pid_t pid;
    char* argv[MAXARGS];
    sigset_t set;
    //前台后台信息，解析命令行参数
    int bg=parseline(cmdline,argv);
    state=bg?BG:FG;

    if(argv[0]==NULL)  //空命令行直接返回
        return;

    if(!builtin_cmd(argv))  //若为非内置命令
    {
        if(sigemptyset(&set)<0)  //初始化信号集合为空
            unix_error("sigemptyset error\n");
        if(sigaddset(&set,SIGINT)<0||sigaddset(&set,SIGTSTP)<0||sigaddset(&set,SIGCHLD)<0)  //将三种信号加入信号集合
            unix_error("sigaddset error\n");
        if(sigprocmask(SIG_BLOCK,&set,NULL)<0)  //阻塞三种信号，避免竞争产生并发错误
            unix_error("sigprocmask error\n");
        
        if((pid=fork())<0)  //创建子进程
            unix_error("fork error\n");

        else if(pid==0)  //子进程
        {
            if(sigprocmask(SIG_UNBLOCK,&set,NULL)<0)  //阻塞信号
                unix_error("sigprocmask error\n");
            if(setpgid(0,0)<0)  //创建新进程组，并将当前进程pid作为进程组id
                unix_error("setpgid error\n");
            if(execve(argv[0],argv,environ)<0)  //加载并运行程序
            {
                printf("%s: Command not found\n",argv[0]);
                exit(0);
            }
        }
        addjob(jobs,pid,state,cmdline);  //将进程加入作业列表
        if(sigprocmask(SIG_UNBLOCK,&set,NULL)<0)  //解除信号阻塞
            unix_error("sigprocmask error");

        if(state==FG)  //若为前台进程则等待其结束并被回收
            waitfg(pid);
        else
            printf("[%d] (%d) %s",pid2jid(pid),pid,cmdline);
    }
    return;
}

/* 
 * parseline - Parse the command line and build the argv array.
 * 
 * Characters enclosed in single quotes are treated as a single
 * argument.  Return true if the user has requested a BG job, false if
 * the user has requested a FG job.  
 */
int parseline(const char *cmdline, char **argv) 
{
    static char array[MAXLINE]; /* holds local copy of command line */
    char *buf = array;          /* ptr that traverses command line */
    char *delim;                /* points to first space delimiter */
    int argc;                   /* number of args */
    int bg;                     /* background job? */

    strcpy(buf, cmdline);
    buf[strlen(buf)-1] = ' ';  /* replace trailing '\n' with space */
    while (*buf && (*buf == ' ')) /* ignore leading spaces */
	buf++;

    /* Build the argv list */
    argc = 0;
    if (*buf == '\'') 
    {
	    buf++;
	    delim = strchr(buf, '\'');
    }
    else 
    {
	    delim = strchr(buf, ' ');
    }

    while (delim) 
    {
	    argv[argc++] = buf;
	    *delim = '\0';
	    buf = delim + 1;
	    while (*buf && (*buf == ' ')) /* ignore spaces */
	       buf++;

	    if (*buf == '\'') 
        {
	        buf++;
	        delim = strchr(buf, '\'');
	    }
	    else 
        {
	        delim = strchr(buf, ' ');
	    }
    }
    argv[argc] = NULL;
    
    if (argc == 0)  /* ignore blank line */
	    return 1;

    /* should the job run in the background? */
    if ((bg = (*argv[argc-1] == '&')) != 0) 
	    argv[--argc] = NULL;

    return bg;
}

/* 
 * builtin_cmd - If the user has typed a built-in command then execute
 *    it immediately.  
 */
int builtin_cmd(char **argv) 
{
    if(!strcmp(argv[0],"quit"))  //内置命令quit退出
        exit(0);
    else if(!strcmp(argv[0],"fg")||!strcmp(argv[0],"bg"))   //内置命令fg or bg调用前后台转换函数
    { 
        do_bgfg(argv);
        return 1;
    }
    else if(!strcmp(argv[0],"jobs"))   //内置命令jobs调用列出作业列表函数
    { 
        listjobs(jobs);
        return 1;
    }
    else if(!strcmp(argv[0],"&"))
        return 1;
   
    return 0;     /* not a builtin command */
}

/* 
 * do_bgfg - Execute the builtin bg and fg commands
 */
void do_bgfg(char **argv) 
{
    struct job_t* job;
    int id;  

    if(!argv[1])  //缺少参数pid直接返回
    {
        printf("%s command requires PID or %%jobid argument\n",argv[0]);
        return;
    }

    if(argv[1][0]=='%')  //是否为作业
    {
        if((id=strtol(&argv[1][1],NULL,10))<=0)  //将操作的进程pid解析到id中
        {
            printf("%s: argument must be a PID or %%jobid\n",argv[0]);
            return;
        }
        if((job=getjobjid(jobs,id))==NULL)  //获取所在作业
        {
            printf("%%%d: No such job\n",id);
            return;
        }
    }
    else
    {
        if((id=strtol(argv[1],NULL,10))<=0)  //将操作的进程pid解析到id中
        {
            printf("%s: argument must be a PID or %%jobid\n",argv[0]);
            return;
        }
        if((job=getjobpid(jobs,id))==NULL);
        {
            printf("(%d): No such process\n",id);
            return;
        }
    }
    
    if(!strcmp(argv[0],"bg"))   //若转为后台进程
    {
        job->state=BG;   //修改状态
        if(kill(-job->pid,SIGCONT)<0)   //给进程组为pid的进程都发送SIGCONT信号
            unix_error("kill error");
        printf("[%d] (%d) %s" ,job->jid,job->pid,job->cmdline);
    }
    else if(!strcmp(argv[0],"fg"))   //若转为前台进程
    {
        job->state=FG;
        if(kill(-job->pid,SIGCONT)<0)
            unix_error("kill error");
        waitfg(job->pid);   //需要等待前台进程终止
    }

    else
    {
        puts("do_bgfg: Internal error");
        exit(0);
    }

    return;
}

/* 
 * waitfg - Block until process pid is no longer the foreground process
 */
void waitfg(pid_t pid)
{
    sigset_t mask;

    if(sigemptyset(&mask)<0)  //将集合初始化为空
        unix_error("sigemptyset error");
    
    while(fgpid(jobs)!=0)   //获取前台进程，若前台进程终止fgpid返回0，循环终止
        sigsuspend(&mask);  //显示的等待信号
    return;
}

/*****************
 * Signal handlers
 *****************/

/* 
 * sigchld_handler - The kernel sends a SIGCHLD to the shell whenever
 *     a child job terminates (becomes a zombie), or stops because it
 *     received a SIGSTOP or SIGTSTP signal. The handler reaps all
 *     available zombie children, but doesn't wait for any other
 *     currently running children to terminate.  
 */
void sigchld_handler(int sig) 
{
    int status,jid;
    pid_t pid;
    struct job_t* job;
    
    if(verbose)  //是否打印详细信息
        puts("sigchld_handler: entering");

    while((pid=waitpid(-1,&status,WNOHANG|WUNTRACED))>0)   //解决信号不排队问题，回收终止的子进程，当所有子进程都终止且被回收时pid=-1退出循环
    {
        if((job=getjobpid(jobs,pid))==NULL)
        {
            printf("Lost track of (%d)\n",pid);
            return;
        }
        jid=job->jid;

        if(WIFSTOPPED(status))  //若进程被暂停
        {
            printf("Job [%d] (%d) stopped by signal %d\n",jid,job->pid,WSTOPSIG(status));  //打印进程信息和导致暂停的信号编号
            job->state=ST;
        }

        else if(WIFEXITED(status))  //若进程调用exit退出或从main返回
        {
            if(deletejob(jobs,pid))  //将进程从作业列表中删除
                if(verbose)  //是否打印详细信息
                {
                    printf("sigchld_handler: Job [%d] (%d) deleted\n",jid,pid);
                    printf("sigchld_handler: Job [%d] (%d) terminates OK  (status %d)\n",jid,pid,WEXITSTATUS(status));
                }
        }
        else  //其他终止状态
        {
            if(deletejob(jobs,pid))
            {
                if(verbose)
                    printf("sigchld_handler: Job [%d] (%d) deleted\n",jid,pid);
            }
            printf("Job [%d] (%d) terminated by signal %d\n",jid,pid,WTERMSIG(status));
        }
    }
    if(verbose)
        puts("sigchld_handler: exiting");
    return;
}

/* 
 * sigint_handler - The kernel sends a SIGINT to the shell whenver the
 *    user types ctrl-c at the keyboard.  Catch it and send it along
 *    to the foreground job.  
 */
void sigint_handler(int sig)  
{
    int olderrno=errno;   //保存errno值
    pid_t pid;
    sigset_t mask_all,prev;
    sigfillset(&mask_all);   //将所有信号加入集合
    sigprocmask(SIG_BLOCK,&mask_all,&prev);  //阻塞信号

    if((pid=fgpid(jobs))!=0)  //找到前台进程
    {
        sigprocmask(SIG_SETMASK,&prev,NULL);   //阻塞信号
        kill(-pid,SIGINT); //给每个前台进程发送SIGINT信号使其挂起
    }

    errno=olderrno;   //恢复errno值
    return;
}

/*
 * sigtstp_handler - The kernel sends a SIGTSTP to the shell whenever
 *     the user types ctrl-z at the keyboard. Catch it and suspend the
 *     foreground job by sending it a SIGTSTP.  
 */
void sigtstp_handler(int sig) 
{
    if(verbose)
        puts("sigstp_handler: entering");

    pid_t pid=fgpid(jobs);   //获取前台作业pid
    struct job_t* job=getjobpid(jobs,pid);  
    

    if(pid)   //找到前台进程
    {
        if(kill(-pid,SIGTSTP)<0)   //给所有前台进程发送SIGTSTP信号
            unix_error("kill (tstp) error");
        if(verbose)
            printf("sigstp_handler: Job [%d] (%d) stopped\n",job->jid,pid);
    }
    if(verbose)
        puts("sigstp_handler: exiting");
    return;
}

/*********************
 * End signal handlers
 *********************/

/***********************************************
 * Helper routines that manipulate the job list
 **********************************************/

/* clearjob - Clear the entries in a job struct */
void clearjob(struct job_t *job)
{
    job->pid = 0;
    job->jid = 0;
    job->state = UNDEF;
    job->cmdline[0] = '\0';
}

/* initjobs - Initialize the job list */
void initjobs(struct job_t *jobs)
{
    int i;

    for (i = 0; i < MAXJOBS; i++)
        clearjob(&jobs[i]);
}

/* maxjid - Returns largest allocated job ID */
int maxjid(struct job_t *jobs)
{
    int i, max = 0;

    for (i = 0; i < MAXJOBS; i++)
        if (jobs[i].jid > max)
            max = jobs[i].jid;
    return max;
}

/* addjob - Add a job to the job list */
int addjob(struct job_t *jobs, pid_t pid, int state, char *cmdline)
{
    int i;

    if (pid < 1)
        return 0;

    for (i = 0; i < MAXJOBS; i++)
    {
        if (jobs[i].pid == 0)
        {
            jobs[i].pid = pid;
            jobs[i].state = state;
            jobs[i].jid = nextjid++;
            if (nextjid > MAXJOBS)
                nextjid = 1;
            strcpy(jobs[i].cmdline, cmdline);
            if (verbose)
            {
                printf("Added job [%d] %d %s\n", jobs[i].jid, jobs[i].pid, jobs[i].cmdline);
            }
            return 1;
        }
    }
    printf("Tried to create too many jobs\n");
    return 0;
}

/* deletejob - Delete a job whose PID=pid from the job list */
int deletejob(struct job_t *jobs, pid_t pid)
{
    int i;

    if (pid < 1)
        return 0;

    for (i = 0; i < MAXJOBS; i++)
    {
        if (jobs[i].pid == pid)
        {
            clearjob(&jobs[i]);
            nextjid = maxjid(jobs) + 1;
            return 1;
        }
    }
    return 0;
}

/* fgpid - Return PID of current foreground job, 0 if no such job */
pid_t fgpid(struct job_t *jobs)
{
    int i;

    for (i = 0; i < MAXJOBS; i++)
        if (jobs[i].state == FG)
            return jobs[i].pid;
    return 0;
}

/* getjobpid  - Find a job (by PID) on the job list */
struct job_t *getjobpid(struct job_t *jobs, pid_t pid)
{
    int i;

    if (pid < 1)
        return NULL;
    for (i = 0; i < MAXJOBS; i++)
        if (jobs[i].pid == pid)
            return &jobs[i];
    return NULL;
}

/* getjobjid  - Find a job (by JID) on the job list */
struct job_t *getjobjid(struct job_t *jobs, int jid)
{
    int i;

    if (jid < 1)
        return NULL;
    for (i = 0; i < MAXJOBS; i++)
        if (jobs[i].jid == jid)
            return &jobs[i];
    return NULL;
}

/* pid2jid - Map process ID to job ID */
int pid2jid(pid_t pid)
{
    int i;

    if (pid < 1)
        return 0;
    for (i = 0; i < MAXJOBS; i++)
        if (jobs[i].pid == pid)
        {
            return jobs[i].jid;
        }
    return 0;
}

/* listjobs - Print the job list */
void listjobs(struct job_t *jobs)
{
    int i;

    for (i = 0; i < MAXJOBS; i++)
    {
        if (jobs[i].pid != 0)
        {
            printf("[%d] (%d) ", jobs[i].jid, jobs[i].pid);
            switch (jobs[i].state)
            {
            case BG:
                printf("Running ");
                break;
            case FG:
                printf("Foreground ");
                break;
            case ST:
                printf("Stopped ");
                break;
            default:
                printf("listjobs: Internal error: job[%d].state=%d ",
                       i, jobs[i].state);
            }
            printf("%s", jobs[i].cmdline);
        }
    }
}
/******************************
 * end job list helper routines
 ******************************/

/***********************
 * Other helper routines
 ***********************/

/*
 * usage - print a help message
 */
void usage(void)
{
    printf("Usage: shell [-hvp]\n");
    printf("   -h   print this message\n");
    printf("   -v   print additional diagnostic information\n");
    printf("   -p   do not emit a command prompt\n");
    exit(1);
}

/*
 * unix_error - unix-style error routine
 */
void unix_error(char *msg)
{
    fprintf(stdout, "%s: %s\n", msg, strerror(errno));
    exit(1);
}

/*
 * app_error - application-style error routine
 */
void app_error(char *msg)
{
    fprintf(stdout, "%s\n", msg);
    exit(1);
}

/*
 * Signal - wrapper for the sigaction function
 */
handler_t *Signal(int signum, handler_t *handler)
{
    struct sigaction action, old_action;

    action.sa_handler = handler;
    sigemptyset(&action.sa_mask); /* block sigs of type being handled */
    action.sa_flags = SA_RESTART; /* restart syscalls if possible */

    if (sigaction(signum, &action, &old_action) < 0)
        unix_error("Signal error");
    return (old_action.sa_handler);
}

/*
 * sigquit_handler - The driver program can gracefully terminate the
 *    child shell by sending it a SIGQUIT signal.
 */
void sigquit_handler(int sig)
{
    printf("Terminating after receipt of SIGQUIT signal\n");
    exit(1);
}
